HGV limits would also rise on dual carriageways under the move, with speed restrictions jumping from 50mph to 60mph.
The Scottish Conservatives said: “For nearly two decades, the SNP have failed to deliver the vital improvements Scotland’s roads need.
“Roads like the A9, A96, A1, A75, A77 and A83 have become notorious for accidents, injuries and deaths.
“But instead of finally taking action to fix Scotland’s roads and protect drivers, the SNP now want to punish them with more restrictions.
“50mph speed limits on single carriageway roads will penalise ordinary people, without cutting down on dangerous driving.
“If the SNP really want to improve road safety, they need to deliver the road upgrades they promised.
“This is just the latest front in the SNP’s war on motorists.”
Transport Scotland has previously stressed the new rules could significantly reduce injury collisions.
They have promised the move would maintain journey times and enhance reliability for motorists regularly using the routes.
Transport Secretary Fiona Hyslop stressed road safety was a “priority” with a commitment to make Scotland’s roads the “safest in the world by 2030”.
The consultation has proved popular, with around 8,700 responses received since it was opened in late November.
She said: “Evidence from the national speed management review indicates that revising speed limits could lead to a significant reduction in the number of injury collisions on our roads while maintaining journey times and enhancing journey time reliability.
“I’d like to thank everyone who has taken the time to engage with the consultation so far, and hope people will take the opportunity to attend these sessions.”